The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
All electric motors, such as alternating current (AC) motors or direct current (DC) function on a principle that two magnetic fields in proximity to one another have a tendency to align. One way to induce a magnetic field is to pass current through a coil of wire. If two coils with current passing through them are in proximity to each other, the respective magnetic fields that are generated have a tendency to align themselves. If the two coils are between 0 and 180 degrees out of alignment, this tendency may create a torque between the two coils. An arrangement where one of these coils is mechanically fixed to a shaft and the other is fixed to an outer housing is known as an electric motor. The torque produced between these coils may vary with the current through the coils.
AC motors may encompass a wide class of motors, including single/multiphase, universal, servo, induction, synchronous, and gear motor types, for example. The magnetic field generated by AC motors may be produced by an electromagnet powered by the same AC voltage as the motor coil. The coils that produce the magnetic field are traditionally called the “field coils” while the coils and the solid core that rotates is called the armature coils.
AC motors may have some advantages over DC motors. Some types of DC motors include a device known as a commutator. The commutator ensures that there is always an angle between the two coils, so as to continue to produce torque as the motor shaft rotates through in excess of 180 degrees. The commutator disconnects the current from the armature coil, and reconnects it to a second armature coil before the angle between the armature coil and field coil connected to a motor housing reaches zero.
The ends of each of the armature coils may have contact surfaces known as commutator bars. Contacts made of carbon, called brushes, are fixed to the motor housing. A DC motor with a commutator and brushes may be known as a ‘brushed’ DC motor, for example. As the DC motor shaft rotates, the brushes lose contact with one set of bars and make contact with the next set of bars. This process maintains a relatively constant angle between the armature coil and the field coil, which in turn maintains a constant torque throughout the DC motor's rotation.
Some types of AC motors, known as brushless AC motors, do not use brushes or commutator bars. Brushed DC motors typically are subject to periodic maintenance to inspect and replace worn brushes and to remove carbon dust, which represents a potential sparking hazard, from various motor surfaces. Accordingly, use of a brushless AC motor instead of the brushed DC motor may eliminate problems related to maintenance and wear, and may also eliminate the problem of dangerous sparking. AC motors may also be well suited for constant-speed applications. This is because, unlike a DC motor, motor speed in an AC motor is determined by the frequency of the AC voltage applied to the motor terminals.
There are two distinct types of AC motors, AC synchronous motors and AC induction motors. A synchronous motor consists of a series of windings in the stator section with a simple rotating area. A current is passed through the coil, generating torque on the coil. Since the current is alternating, the motor typically runs smoothly in accordance with the frequency of the sine wave. This allows for constant, unvarying speed from no load to full load with no slip.
AC induction motors are generally the more common of the two AC motor types. AC induction motors use electric current to induce rotation in the coils, rather than supplying the rotation directly. Additionally, AC induction motors use shorted wire loops on a rotating armature and obtain the motor torque from currents induced in these loops by the changing magnetic fields produced in the field coils.
Conventional electric motor driven vehicles such as golf cars and small utility vehicles are DC powered, and primarily powered by a shunt-type DC drive system. The shunt-type DC motor has replaced many of the older series wound DC motors for powering vehicles such as golf cars. A shunt-type DC motor has armature and field windings connected in parallel to a common voltage source, a configuration which offers greater flexibility in controlling motor performance than series wound DC motors. However, these shunt type motors still present maintenance and potential spark hazard problems. It is not heretofore believed that a brushless AC drive system has been developed which provides the motive force for driving wheels of a vehicle such as a golf car.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.